1. Field of the Invention
The present invention relates to the field of methods for patterning photoresists, and more particularly, to methods for patterning self-developing photoresists.
2. Background Information
Most of the photoresists used in the electronics industry require wet developing steps after having been exposed in a desired pattern in order to wash away the soluble portion of the resist. Such wet processing is undesirable in many applications.
Consequently, another class of photoresists known as self-developing photoresists was developed. These materials include such materials as poly(butene-1-sulfone) and nitrocellulose. These self-developing photoresists, when exposed to an appropriate energy source which may include ultraviolet light, excimer lasers, ion beams and electron beams, absorb the incident beam. The absorbed energy is sufficient to break chemical bonds and cause decomposition of the surface portion of the layer of self-developing photoresist into volatile species which are carried away from the substrate on which the photoresist is disposed. In the case of nitrocellulose, the volatile products reported by T. F. Deutsch and M. W. Geis in, "Self-Developing UV Photoresist Using Excimer Laser Exposure", Journal of Applied Physics, Vol. 54 (12), pp 7201-7204 (1983), include CO, CO.sub.2, H.sub.2 O, H.sub.2, N.sub.2 and NO. Additional information about self-developing photoresists is provided in the paper "Self-Developing Resist with Submicrometer Resolution and Processing Stability", by M. W. Geis, et al., Applied Physics Letters Vol.43 (1), pp 74-76 (1983). Each of these papers is incorporated herein by reference in its entirety. When sufficient energy is directed to a particular portion of the photoresist, it is possible to remove the full depth of the photoresist to leave the underlying material exposed. Thereafter, process steps such as etching or plating may be performed which will be selective to the exposed portion of the substrate. Where etching is performed by a dry process such as plasma or reactive ion etching, the entire process may be carried out without the use of wet solutions. Alternatively, a wet etching or plating solution may be used as desired.
A problem which has existed in the photolithographic arts is the problem of producing a photolithographic pattern on the inside of a tubular member. As the inner diameter of the tubular member decreases, photolithographic provision of a pattern on the inner surface of that tubular member becomes increasingly difficult. The related patent application Ser. No. 290,950, entitled "Electromagnetic Transducers and Method of Making Them"by Y. S. Liu et al. discusses the needs for tubes of this type and the problems involved in their fabrication in greater detail and discloses one technique for producing patterns on the inside of a tubular member. Further improvements in methods of forming such patterns would be desirable.
While self-developing photoresists have provided increased versatility in processing for the electronics and other arts, further versatility is desirable.